Automated sizing equipment segregate incoming lots into various size categories. Agricultural items such as fruits and vegetables are segregated into various size and color groupings for later packaging, or processing, distribution and eventual sale on the retail level. Such segregation is important since packaged items of a certain "size" may have a different value than a package of a different "size." Additionally, since lot dollar value depends on the item size distribution, growers are paid depending upon the number of items in each category.
Size groupings may be based on number of items per volume--such as number per box, with box weight open--or number per pound--that is, number per box at a fixed weight. Typically, limits are placed on the maximum and minimum variation in fruit size and weight allowable within one box. In addition, where products are packed according to a given number per carton, a minimum weight limit is usually placed on the total carton. In order to account for the fluctuation item size, conventional mechanical sizers must be adjusted to provide for somewhat oversized fruit in order to assure that the minimum poundage per package requirement in met. For example, if 40 pounds per carton is the minimum acceptable weight, it may be that conventional sorting machinery must be set for an average of 411/2 pounds to assure that each carton weighs at least 40 pounds. Consequently, a substantial amount of the items are essentially given away.
The reasons for this inaccuracy in conventional weighing systems vary with the type of system. For example, for mechanical sizers using physical dimensions such as diameter, variation could be due to changes in either shape or density within the lot of items to be sorted or from lot to lot. For mechanical spring weighing sizing systems, temperature change, the large number of scales required, vibration, and item positioning may cause inaccurate segregation. With either type system, the inaccuracies inherent in the system itself require that a substantial amount of fruit be given away.